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To: Kris Kennaway <kris@obsecurity.org>
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Comments: In-reply-to Kris Kennaway <kris@obsecurity.org>
	message dated "Tue, 10 Apr 2007 14:43:33 -0400"
Date: Tue, 10 Apr 2007 14:46:56 -0400
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From: Tom Lane <tgl@sss.pgh.pa.us>
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Cc: performance@FreeBSD.org, current@FreeBSD.org,
	Mark Kirkwood <markir@paradise.net.nz>,
	pgsql-hackers <pgsql-hackers@postgresql.org>
Subject: Re: [HACKERS] Anyone interested in improving postgresql scaling? 
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Kris Kennaway <kris@obsecurity.org> writes:
>>> Make SYSV semaphores less dumb about process wakeups.  Currently
>>> whenever the semaphore state changes, all processes sleeping on the
>>> semaphore are woken, even if we only have released enough resources
>>> for one waiting process to claim.

>> Correct.  The behavior Kris describes is surely bad, but it's not
>> relevant to Postgres' usage of SysV semaphores.

> Sorry, but the behaviour is real.

Oh, I'm sure the BSD kernel acts as you describe.  But Mark's point is
that Postgres never has more than one process waiting on any particular
SysV semaphore, and so the problem doesn't really affect us.

Or do you mean that the kernel wakes all processes sleeping on *any*
SysV semaphore?  That would be nasty :-(

			regards, tom lane